This invention relates generally to self propelled irrigation systems and more particularly to self propelled center pivot irrigation systems.
In areas where large sections of land must be irrigated to be productive various sprinkler arrangements have proven to be the most effective in many situations. In recent years it has been found that the most inexpensive and effective of these sprinkler irrigation systems has been the self propelled center pivot systems. In this type of system the fixed center pivot is connected to a radially extended irrigation pipeline. The pipeline is mounted on a series of wheel mounted moveable carriages at intervals of several rods. The carriages act as support for the irrigation pipeline and also propel the pipeline around a circular path. Generally the moveable carriage which is at the farthest end of the pipeline is in continuous motion and the remaining carriages are moved only when they are sufficiently out of line with the next more radially remote carriage. The carriages are generally propelled by electrical drive motors which are actuated by an alignment sensing means. The alignment sensing means is usually an electrical stress gauge or similar electrical device which measures the deflection of the pipeline from the norml perpendicular alignment.
The advantages of a self propelled system over manually moved irrigation pipes is quite obvious. The primary advantage of a self propelled center pivot irrigation system over self propelled linear irrigation systems is, of course, a reduction in the length of pipeline and a reduction in the number of motor driven carriages necessary to cover the same amount of ground. However, an inherent disadvantage of the center pivot irrigation system when working on noncircular fields is that the corner sections of the field tend not to receive any irrigation water. Another problem which needs to be overcome is the disturbance of the land caused by the carriages. The weight of the electrical motors and reduction gear accentuates this problem. An associated problem having to do with the use of electrical motors and electrical alignment devices generally is the expense of this equipment and the danger of severe electrical shock caused by using electrical apparatus under wet conditions.
A great number of patents have been issued dealing with these and other problems associated with center pivot irrigation systems.
Reinke U.S. Pat. No. 3,912,170 describes the use of light weight aluminum irrigation pipe in center pivot irrigation systems wherein steel support wires are used to give the system the necessary structural strength.
Reinke U.S. Pat. No. 3,623,662 discloses the center pivot irrigation system using a worm gear drive assembly for driving the moveable carriages and also discloses an alignment sensing means whereby an electric circuit is completed by the deflection of an irrigation pipe connection plate which actuates an electric drive motor.
Kricher et al. U.S. Pat. No. 3,797,517 and Seckler et al U.S. Pat. No. 3,802,627 disclose a self propelled irrigation apparatus for watering noncircular areas wherein a carriage supported deflection arm is pivoted on the main irrigation pipeline. Stress gauges and a computer operated angle encoder are used to control movement of the deflection arm to water noncircular portions of a field.
Reinke U.S. Pat. No. 3,608,826 and Reinke U.S. Pat. No. 3,750,953 both disclose the use of a cam actuated end gun for irrigating the corners of noncircular fields. A cam device mounted near the center pivot opens a control circuit which actuates a solenoid valve to provide water to the end gun.
Zybach U.S. Pat. No. 2,941,727 discloses a float operated water flow sensing device which may be situated at a number of positions along the pipeline which uses a mercury switch for activating a control circuit to turn off the pump during low flow conditions at any point along the pipeline. A water actuated piston cylinder drive means is also disclosed. Use of a wire connected to one side of an irrigation pipe and also connected to a moveable carriage as an alignment sensing means is also disclosed.
Although the above cited art represents an advance over prior art a number of the more important problems remain unsolved. An effective drive means for the moveable carriages which does not employ expensive and heavy electric motors has not yet been disclosed. The water piston device disclosed by Zybach involves a number of complicated and expensive moving parts which will present a maintenance problem. The water piston device is also extremely heavy adding to the compaction problems already present in the motor driven carriages. The computer operated pivot arm of Kricher and Seckler offers an overly complicated and expensive method of providing water to the noncircular corners of fields. Although the solenoid actuated end gun of Reinke provides a preferable solution to the watering of corners in a field, the undesirable feature of having an electric cable stretching along the length of the pipe remains uncorrected. Another problem which needs to be addressed is a need for safety devices to stop the operation of carriages when misalignment becomes sufficient to cause damage to the irrigation pipeline.